[kh99]

Sorry for the late reply, but if you're still looking for this, I think you can do something like:

SELECT COUNT(*) FROM post 
   WHERE userid = X AND visible = 1 AND
      dateline >= UNIX_TIMESTAMP('2013-01-01 00:00:00') AND
      dateline <= UNIX_TIMESTAMP('2013-06-01 23:59:59')

where of course you'd change X to the userid you want, and change the dates as needed.